WEST CHESTER, Pennsylvania (CNN) -- When Nicholas Berg took an Oklahoma bus to a remote college campus a few years ago, the American recently beheaded by terrorists allowed a man with terrorist connections to use his laptop computer, according to his father.

Michael Berg said the FBI investigated the matter more than a year ago. He stressed that his son was in no way connected to the terrorists who captured and killed him.

Government sources told CNN that the encounter involved an acquaintance of Zacarias Moussaoui -- the only person publicly charged in the United States in connection with the September 11, 2001, terror attacks.

According to Berg, his son was taking a course a few years ago at a remote campus of the University of Oklahoma near an airport. He described how on one particular day, his son met "some terrorist people -- who no one knew were terrorists at the time."

At one point during the bus ride, Berg said, the man sitting next to his son asked if he could use Nick's laptop computer.

"It turned out this guy was a terrorist and that he, you know, used my son's e-mail, amongst many other people's e-mail who he did the same thing to," Berg said.

Government sources said Berg gave the man his password, which was later used by Moussaoui, the sources said.

The sources said the man who used Berg's e-mail knew Moussaoui, now awaiting trial on federal charges that could bring a death sentence. But the sources would not disclose details of how the men were connected.

Moussaoui, 36, was arrested in August 2001 after he aroused suspicion at a Minnesota flight school when he arrived for 747 simulator training without holding a pilot's license. A French national of Moroccan descent, Moussaoui has admitted in open court that he belonged to al Qaeda, the radical Islamic group behind the September 11 attacks, which killed nearly 3,000 people.

But Moussaoui has fiercely denied being involved in the September 11 plot, and the prosecutors' theory of his role has shifted from being a possible 20th hijacker that day to possibly piloting a fifth hijacked jetliner targeting the White House.

Berg said his son cooperated fully with an FBI investigation into the matter.

"He was happy to cooperate, and that was never an issue," he said. He emphasized that the individual was not a friend of his son's or even an acquaintance -- "just a guy sitting next to him on the bus."

"Whoever was next to my son was treated with great respect and friendship. Like I said, he knew no dangers from people. The FBI were satisfied with that."